1. Technical Field
The technical field relates to a composite electrode and an electrolytic capacitor.
2. Background
Improving the electrolyte conductivity has long been one of the major topics in the development of an electrolytic capacitor. The electrolyte with a high conductivity can reduce the equivalent series resistance (ESR) of the electrolytic capacitor, so as to provide high reliability and low impedance at high frequency. A conductive polymer has a higher conductivity than a liquid electrolyte or a solid organic semiconductor complex salt (e.g. tetracyanoquinodimethane (TCNQ) complex salt) used for conventional capacitors, and exhibits an adequate insulating property at high temperature. Besides, the conductive polymer is safe and free of explosion of a liquid capacitor caused by liquid evaporation. Therefore, such conductive polymer has become the mainstream of the solid electrolyte for existing electrolytic capacitors.
In recent years, high voltage conductive polymer capacitors have been widely applied in vehicles. The reliability of the high voltage conductive polymer capacitors is poor for some reasons. First, when the material of the oxide layer is aluminium oxide formed by anodization, the aluminium oxide layer is inhomogeneous. Therefore, cracks are easily generated at grain boundaries so as to cause a leakage current. Besides, the conductive polymer has poor film properties and is highly brittle. In long-term use, the vibration from the environment causes deformation of the conductive polymer and breakdown of the oxide layer. Moreover, the conductive polymer has poor film foil ling property and therefore is not able to completely cover the surface of the oxide layer of the capacitor, resulting in a high leakage current, a high impedance and a low yield of the capacitor. The said reasons cause a significantly high leakage current and even a short circuit, and the yield of the high voltage capacitor is accordingly reduced.